Add `SqliteStore::code_lang_breakdown()` that queries
`json_extract(metadata_json, '$.code_lang')`, groups by it, and
skips NULL rows — returning `BTreeMap<String, u32>`.
Wire it into `collect_stats` in `kebab-app::schema`, replacing the
`BTreeMap::new()` placeholder inserted by 1A-1.
Test: `store::tests::code_lang_breakdown_counts_by_code_lang` asserts
rust=1 and that a null-code_lang doc does NOT appear in the map.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
altair823
da51e59081